It has become common place to transport data across air interfaces. In most such situations, bandwidth becomes a factor either because a single user (such as a PC) is trying to move large data files in a given period of time or several users are trying to use the same air interface to move smaller files.
Many data transportation protocols are now in use, some of which deal with wireline interconnections (such, for example, the 802.3 protocol) and some of which deal with air interface transmissions (such as, for example, 802.16). These protocols have several layers, including the physical layer and several operational layers. Each such layer is designed to accomplish a certain objective and each such layer requires a certain format of data. For example, in addition to transportation of the payload (typically data), address information must be included as a header so that the payload can be delivered to the proper destination. In some situations, it is necessary to use additional protocols for specific purposes. When this is necessary, the additional protocol adds overhead (data bits) to the communication payload.
One example of the problem is when an Ethernet header is necessary on a packet to deliver the packet to a particular location within, for example, a local area network. The overhead from the header is not a problem for those portions of the communication channel (for example, the wireline portions) where bandwidth is essentially unlimited. However, when the communication must pass across an air interface using a specific protocol, such as, for example, the 802.16 protocol, the addition of the Ethernet address in the protocol is a burden on the air interface as it adds bytes (typically 14 bytes). These extra bytes are overhead to the data being transferred across the air interface and in many situations is excessive, particularly for low data rate transfers.
One solution to the problem is to carry the IP on top of an IP convergence sub-layer (IPCS) which would then naturally fall on top of the 802.16 frame in Layer 3. The advantage of such an approach is that it is very efficient because it is IP on top of IP with no additional overhead, or very little additional overhead. The downside is that Layer 3 is designed to carry network routing data and data loads and thus network administrators are not willing to be impacted by the overhead of managing very large (in terms of data flow) Layer 3 traffic. Such a network architecture would be unyielding and difficult to deploy in practice.